1. Filed of the Disclosure
This disclosure relates to pulsed lasers. More particularly, the disclosure relates to injection seeding employed to achieve stable output generated by a single mode fiber laser and characterized by confined spectrum bandwidth and high peak pulse power or high power for a source with continuous power.
2. Discussion of the Prior Art
Master-slave laser systems with relatively high output energies and narrow linewidths are widely used in a variety of industries. Typically, these systems include a laser cavity wherein longitudinal modes oscillate to stimulate output. To meet a variety of requirements, these systems are configured to operate in single or multimode regimes. In multimode operation, more than one longitudinal mode oscillates. In single mode operation, predominantly one longitudinal mode oscillates within the cavity.
One realization of the above-disclosed systems typically may include a seed source—master oscillator—generating weak radiation, known as seed radiation, which is coupled into the laser cavity of a slave oscillator. As a result, the seed radiation excites one or more longitudinal modes within the cavity of the slave laser.
Laser systems are often required to radiate, among others, a stable output, controlled wavelength, high peak power pulse width narrow frequency bandwidth. By controlling the spectral properties of a slave oscillator by a seed oscillator the above listed objectives can be effectively attained.
Single longitudinal mode injection seeding has long been utilized as an effective process for generating radiation characterized by substantially single transverse and longitudinal mode. The degree of “substantiality” is somewhat subjective.
The output of a typical master-slave semiconductor laser system is characterized by one dominant mode and side modes at the output of the slave oscillator. While the radiation spectrum is broader than the single frequency output of the master oscillator, it is still often referred to as a substantially SM radiation, which is widely accepted. The ratio between the peaks of respective dominant and side modes is a good indicator of how “substantially” single “moded” the radiation is. Referring hereinafter to this ratio as a side-mode suppression ratio (SMSR), as far as Applicants are aware of, the 30 dB SMSR is considered excellent.
However, in case the slave radiation is further amplified in the fiber amplifier to the power level (peak power) above 100 W, the spectra of the amplified radiation at the output of the amplifier is substantially wider than the slave radiation at the input of the amplifier. As a consequence, the bandwidth of the pulse emitted by the fiber amplifier will be pretty far from the single-mode radiation, have much broader spectrum than that one of the slave radiation at the input of the amplifier at so much that in certain situations the output amplified radiation may have more than one mode. As one of ordinary skills readily understands, the broadening of the radiation is explained by nonlinear process occurring in a fiber.
With the broad amplified spectrum at the output of the amplifier an SMSR associated with dominant and side modes of the amplified output radiation radically lowers. Hence, the SMSR of the slave radiation should be substantially greater than what is now considered acceptable in order to have the desired value thereof at the output of fiber amplifier.
A need, therefore, exists for a method and device operative to generate a substantially SM slave radiation having an SMSR exceeding 40 dB at the input of a single mode fiber amplifier.
A further need exists for a method and apparatus for generating a narrowed broadband slave spectra at an input of SM fiber laser which is amplified in a SM fiber laser so that a broadband amplified spectra at the output of the amplifier is substantially the same as the slave spectra at the input of the amplifier.